Short-circuiting device for electric motors



Dec. 13, 1927.

C. L. KENNEDY SHORT CIRCUITING DEVICE FOR ELECTRIC IOTORS led Ma 25,1927 Patented Dec. 13, 1927.

UNITED STATES 1,652,482 PATENT OFFICE...

I CARLTON L. KENNEDY, OF BRAIN TEEE,1VIASSACHUSETTS, ASSIGNOR TO THEHOLTZER- CABOT ELECTRIC COMPANY, ROXBURY, MASSACHUSETTS, A CORPORATIONOF MASSACHUSETTS.

SHORT-CIRCUITING DEVICE FOR ELECTRIC MOTORS.

Application filed May 25, 1927. Serial 1T0. 194,026.

The present invention relates to improve ments in short-circuit ngdevices for electric motors, and more particularly to induction motors.

The invention constitutes an improve ment on the construction of theKennedy Patent No. 1,145,59d, dated July 6, 1915.

In the accompanying drawings illustrat ing the preferred form of theinvention, Fig. 1 is an end elevation of a. commutator with the improvedshort-circuiting devices applied thereto; Fi 2 is an axial section ofthe commutator showing the short-circuiting devices in operativeposition; Fig. 3 is a similar section with the short-circuiting devicesinoperative; Fig. a is a perspective View of a contact; and Fig. 5 is aperspectiveview of the lever. devices.

The illustrated embodiment of the invention is described as follows: Thecommutator segments are mounted upon a commutator spool 11 which isrigidly secured to the rotor shaft 12. The inner end of the spool has anoutwardly projecting flange or lip 18, having a beveled inner face. Theinner end of the periphery of the spool carries a ring or follower 1 1,which has a beveled inner face similar" to that of the flange 13, and itis secured in place by spinning a thin lip of the spool over the outsidesurface of the ring 14. The commutator segments are firmly positionedbetween the lip or flange 13 of the ring 14;, being insulated from themin the usual manner.

Between the commutator spool and the rotor shaft is formed a contactcarrier or rocker arm chamber 16. Within this cham her are received therocker arm devices shown in Fig. 5 andindicated in a general way by thereference character 17. In the construction shown in the drawings eightof these rocker arm devices are employed. Each device has a base 18,having a curved edge at 19 to fit the rotor shaft, and two arms 20 and21 which extend at right angles from the base 18 outwardly, as shown inFigs. 2 and 8. The ends of these arms carry hooks 22 upon which thecontact blocks 23, shown in Fig. 4, are supported.

The rocker arm devices are arranged in the rocker arm chamber with theirbases radially arranged around the shaft. The inner ends of the basesare engaged by the washer 24:, which embraces the shaft and is forcedtoward the bottom of the rocker chamber by the spring 25, the outerabutment of which is formed by the nut 26 first turned to. the correctlyadjusted position, and then secured in such position by prickpunchingthe threadso the nut cannot work loose.

The pressure of the rocker spring nor mally tends to hold the rockersinthe position shown in Fig. 3. Upon the hooks of the rocker arms aresupported the contact blocks 23. There are sixteen of these bloc (S,

one for each hook of the rocker arm devices. These contact blocks aremade of sheet copper stamped and formed in the shape illustrated. Thecontact blocks consist of two radiating contact members 27 extendingfrom the base 28, provided with a hole 29 which slips over the hook 22.Each contact member is provided with a protuberant contact portion 30.As seen in Fig. 2, the contact block is so supported on the carrier thatthe point 31 of the hookengages the inner margin of the base 28 of theblock, as a consequence of which; when the shaft rotates at any speedbeyond the critical speed, the contact block assumes the position shownin Fig. 2, and the contact portions of the radiating members of theblock engage the commutator segments 10, thereby short-circuiting thecommutator at a large number of points, as shown.

This construction of short-circuiting de vice has all of the goodfeatures of operation which the construction of the Kennedy patentreferred to has, and in addition it is much lighter, cheaper, simplerand more durable. Thus, the rocker arm devices are made of stamped sheetmetal whereas the rocker arms of the patent are made of castings andrequired to be machined. Again, the contact blocks of the presentconstruction are similarly made of stamped sheet metal, which is muchless expensive than the cast contact blocks of the patent. Furthermore,the use of a pivot pin in the patent construction requires the drillingof holes and the fitting and riveting of the pins or pintles in place,whereas in the present construction the contact blocks are merely hookedon the hooks of the rocker arm devices before the devices are moved intothe rocker arm chamber. The pivot of the contact blocks of the patentoccupies a position very much the same as that of the position of thepoint of the hook of the rocker arms of the resent construction, and theoperation of tiie devices is the same in that when the motor is at rest,the rocker arm devices and contact blocks occupy the position shown inFig. 3. After the rotation begins centrifugal force causes the contactblocks immediately to assume the position shown in the lower part ofFig. 3, and then when the critical speed is reached, the rocker armdevices move outwardly to the position shown in Fig. 2, and the blocksthen occupy the position shown in Fig. 2, short-circuiting thecommutator. The outward throw of the rocker arm devices is limited bytheir engagement with the inner wall of the rocker arm chamber, and whenthe parts have assumed the position just described the motor operates asan induction motor.

As in the construction of said patent, by properly adjusting thestrength and tension of the spring 25 to the weight of the contactblocks and the weight of the rocker arms,

' the centrifugal force due to the outward travel of the blocks may bemade to increase faster than the increase in the tension of the spring,with the result that the blocks will attain a short-circuiting positionon the commutator by a quick movement.

Having thus described the invention, what is claimed is:

1. A short-circuiting device for electric motors having, in combination,a plurality of tippingly mounted rocker arm levers each provided with ahook, and a contact block loosely hung on the hook adapted to engage thecommutator.

2. A short-circuiting device for electric motors having, in combination,a plurality of pairs of-tippingly mounted rocker arm levers eachprovided with a base and with a hook, and a contact block having a holeto receive the hook on which the block is loosely hung.

3. A short-circuiting device for electric motors having, in combination,a plurality of tippingly mounted rocker arm devices con'iprising a base,two arms arranged at right angles to the base, the arms provided. ontheir ends with hooks, and a contact block comprising a base providedwith a hook hole and two radiating contact members extending outwardlyfrom the base.

4. A short-circuiting device for electric motors having, in combination,a plurality of tippingly mounted rocker arm devices each provided with abase having arms ex tended substantially at right angles thereto locatedbetween the ends of the base, a rotor shaft, a spring encircling theshaft adapted to engage one end of the bases of the rocker arm devices,normally acting to hold the latter in position with their arms extendingparallel with the shaft, the rocker arms being provided on their outerends with outwardly extended portions having hooks on their ends andContact blocks hung upon the hooks.

In testimony whereof I have signed my name to this specification.

CARLTON L. KENNEDY.

